gradle: update to 8.7

3 years of active development.

Notable updates between major versions:
7 -> 8:
- upgrades the Kotlin DSL's API level to Kotlin 1.8.
- configuration cache speeds up builds by executing more tasks in
  parallel.
- gradle user home can be managed by configuring the retention time of
  cache directories.
  - Cache cleanup can also be disabled.
- many bug fixes and other general improvements.

6 -> 7:
- enabled file system watching by default to make your incremental
  builds faster
- support Java 16
- adds support for building on Macs using Apple Silicon processors.
- feature preview for centralized dependency versions
- enables build validation errors to make your builds more reliable
- easier to create convention plugins for settings files.
- many incubating features have been promoted to stable.

Major and minor release notes:
https://docs.gradle.org/8.7/release-notes.html
...
https://docs.gradle.org/8.0/release-notes.html

https://docs.gradle.org/7.6/release-notes.html
...
https://docs.gradle.org/7.0/release-notes.html

https://docs.gradle.org/6.9/release-notes.html


(ktnb)